Electromagnetic induction apparatus



Dem. 9,1947. sHQR- 2,432,343

ELECTROMAGNETIC INDUCTION APPARATUS Filed Feb. 1, 1945 Fig. I.

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Locus or E3 nRc ABOUT 0 Inv who? 5 Thomas T Short y %7 His Attorney.

Patented 9, 1947 APPARATUS Thomas T. Short, Fort Wayne, Ind., assignorto General Electric Company, acorporation of New York ApplicationFebruary 1, 1945, Serial No. 575,649

This invention relates to electromagnetic induction apparatus and moreparticularly to improvements in static constant voltage transformers.

By a "static constant voltage transformer is meant a device which withno moving parts converts a variable alternating supply voltage to analternating output voltage which is substantially constant over anappreciable range of variation of output current and input voltage. Manydevices of this kind are available both in the litera ture and on themarket.

This invention is characterized by input an output circuits which arecoupled by means of a unitary magnetic core in such a manner that anabnormally high leakage reactance exists between the circuits and acompensating voltage which is proportional in magnitude and phase withthe leakage reactance voltage drop between the two circuits is insertedin the output circuit.

An object of the invention is to provide a new and improvedelectromagnetic induction apparatus.

Another object of the invention is to provide a new and improved staticconstant voltage transformer.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

In the drawing Fig. 1 is a sectional view of the transformer portion ofan embodiment of the invention, Fig. 2 is a circuit diagram of anembodiment of the invention utilizing the structure shown in Fig. 1,Fig. 3 is a vector diagram illustrating the operation of the inventionat full load unity power factor and with varying input voltage, and Fig.4 is a vector diagram illustrating the operation of the invention withfixed input voltage and varying load.

Referring now to the drawing and more partlcularly to Fig. 1, there isshown therein a magnetic core I of the forced core type having integralmagnetic shunts 2, although it will be obvious to those skilled in theart that the core may be of the interleaved type with inserted shunts,if desired. The magnetic shunts are provided with air gaps 3 for reasonswhich will be explained more fully below. Mounted on the core with themagneticshunts between them are a primary winding 4 and a secondarywinding 5. A compensating winding 6, the purpose of which will also bedescribed below, is wound on the magnetic shunts.

The primary and secondary fluxes are prefer- 3 Claims. (01. 32360) ablysubstantially equal but the maximum secondary flux density issubstantially higher than the primary flux density. This is accomplishedby making the sections of the core traversed by the primary and secondfluxes of substantially equal area and providing the portion of the corewhich is traversed by the secondary flux with restricted sections 1.Thes sections are saturated during normal operationof the device whilethe main portion of the secondary section is not saturated. I

As shown in Fig. 2, the prim'ary winding 4 is connected to inputterminals, the voltage between which is E0, and the compensating winding6 whose voltage is E2 is connected in series with a portion of thesecondary winding 5 whose voltage is E1 between ,a pair of outputterminals, the voltage between which is E3. Also, a capacitor 8 iscoupled to the secondary winding and, as shown,

it isconnected across the entire winding. However, it will be obvious tothose skilled in the art that capacitor 8 could be coupled to thewinding A whose voltageis E1 by connecting it across another windingwhich is closely coupled thereto.

The capacitor 8 is of such a value that with the output circuit open thecapacitor 8 and the secondary winding are tuned to near resonance. Inother words, the capacitor supplies the exciting current required tooperatethe restricted section at saturation. This providesa relativelystable secondary voltage- With this condition the flux through the shuntis small at no load and m creases rapidly with increasing load.

The operation or the illustrated'embodimentof causeof the saturation ofthe portion of the core traversed by the secondary flux, that is to say,by the saturation of the restricted sections 1. The vector difierencebetween the corresponding E0 and E1 vectors is the leakage reactancevoltage drop of the transformer, and the air gaps 3 of Fig. 1 are soproportioned that the phase displacement between the E0 and E1 voltageswill be in the range of 30-40 degrees at full load unity power factor.The voltages E2-1, EM and E2-3 are the corresponding voltages of thecompensating winding 6. As th vector sum of thesecondary voltage and theleakage reactance voltage drop equals the input voltage, it will be seenthat the E: voltages are opposite in phase to the leakage reactancevoltage. By properly proportioning the compensating winding 6 the vectorsums of the E1 and E: voltages may be made to terminate on an arc of acircle whose center is at I in Fig. 3 and this are will be the locus ofthe output voltage E3 as it will be seen from Fig. 2 that Ea=Ei+Ez andFig. 3 shows how these voltages add vectorially.

It will be noted that the compensating action of E: in Fig. 3 is dueprimarily to its shift in phase with changes in input voltage ratherthan to changes in its magnitude. Ordinarilythe magnitude of the voltageE: will be of the order of 10-20 per cent of E: at full load.

Referring now to Fig. 4, the values M31 and E2 at no load, half load andfull load for a constant value of input voltage Eo are shown. It will beobserved that again the E: vectors terminate on an arc of a circle aboutpoint so that E: is substantially constant throughout the full range ofload, which load is preferably a unity power factor load. In Fig. 4 itwill be observed that the compensating action of E2 is due primarily toits change in magnitude with changes in load magnitude rather than tochanges in phase of this voltage with changes inload magnitude.increasin phase displacement between E0 and E1 with increases in load isof course due to the increase in leakage flux due to the increased loadcurrent, which increased leakage flux produces an increased leakagereactance voltage.

It will of course be understood that the abovedescribed constant voltagetransformer may be provided with a suitable harmonic filter or frequencycompensator or power factor compensator or any combination thereof.

While there has been shown and described a particular embodiment of thisinvention, it will be obvious to those skilled in the art that variouschanges and modifications can be made therein without departing from theinvention and, therefore, it is aimed in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A constant voltage transformer comprising, in combination, a unitarymagnetic core having a primary winding receiving section, a secondarywinding receiving section and a magnetic shunt between said' sections,primary and secondary windings on their respective core sections, acompensating winding on said magnetic shunt connected in series with a.portion of said secondary 2. A constant voltage transformer comprising,

in combination, a' unitary magnetic core having a primary windingreceiving section, a secondary winding receiving section and a magneticshunt between said sections, primary and secondary windings On theirrespective core sections, a compensating winding on said magnetic shuntconnected in series with a portion of said secondary winding, and acapacitor connected across said secondary winding, -said secondarywinding re- The' 7 Number ceiving section having a normally'saturatedrestricted section, said coresections normally carrying substantiallyequal flux and having substantially equal cross sectional areas exceptfor said restricted section, said compensating winding having a voltageof 10-20 per cent of the output voltage of said transformer.

3. A constant voltage transformer comprising, in combination, a unitarymagnetic core having a primary winding receiving section, a secondarywinding receiving section and a magnetic shunt between said sections,primary and secondary windings on their respective core sections, acompensating winding on said magnetic shunt connected in series with aportion of said secondary winding, a capacitor connected across saidsecondary winding, said secondary winding receiving section having anormally saturated restricted section, said core sections normallycarrying substantially equal flux and having substantially equal crosssectional areas except for said restricted section, and an air gap insaid magnetic shunts so "proportioned that the leakage reactance of saidtransformer displaces the primary and secondary voltages ofsaidtransformer by 30-40 degrees at full load, said compensating windinghaving a voltage of 10-20 per cent of the output voltage of saidtransformer at full load.

THOMAS T. SHORT.

' REFERENCES crrnn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date 1,599,570 Lucas Sept. 14, 1926 2,143,745Sola Jan. 10, 1939

